Charles Koch, the conservative political activist and industrial magnate, is 77 years old. Forbes estimates his fortune at $34 billion. When I met him at his book-crammed office in Wichita, Kan., a few weeks ago, I asked why he was still working.

Artificial intelligence experts say they have mastered a version of a popular poker game called Texas Hold ’em—an advance in game theory that could lead to broader innovations in military strategy, national security, decision-making and auctions.

The U.S. still has the highest incarceration rate in the world, but it has dropped in recent years. A new study shows that repetition improves your performance more with sports and games than with book learning. And fewer riders are dropping out of the Tour de France than ever before.